the word 'thirstily' is built upon the old english noun þurst, which denotes a condition of dryness and a craving for drink. this germanic root is ancient, traceable back to proto-indo-european ters- ("to dry"), a sense vividly preserved in the modern meaning. the adjectival form 'thirsty' emerged in old english, and the adverb was subsequently formed by adding the prolific old english adverbial suffix '-ly', which indicates manner. thus, the literal construction "in a thirsty manner" logically evolved to describe both the physical act of drinking eagerly and, by metaphorical extension, any intense and eager desire.

Structure: thirst (dryness, desire for drink) + i (connective) + ly (adverb suffix) thirst: from old english þurst, þyrst, meaning "dryness, thirst". it is a germanic root. i: a connective vowel used in english word formation, often of latin or greek origin but here serving to join the root to the suffix. ly: from old english -līce, an adverb-forming suffix meaning "in a manner of".